A number of hydroconversion processes are well known in the art. One of these, hydrocracking, is becoming increasingly important since it provides hydrocarbon product of good quality with considerable flexibility of product type. A specific use of hydrocracking processes and the catalysts useful therein is the conversion of rather heavy hydrocarbon feedstocks to more useful products of lower molecular weight. Historically, catalytic hydrocracking was used to increase the production of relatively low boiling materials such as gasoline. More recently, however, hydrocracking is also employed in the production of middle distillates.
To obtain hydrocracking catalysts particularly useful in processes for production of middle distillates, catalysts have been developed based on zeolite materials as modified by techniques such as ammonium ion-exchange and calcination to improve the performance of the zeolite catalysts.
One zeolite considered to be a good precursor of hydrocracking catalysts is the well-known synthetic zeolite Y as described by U.S. Pat. No. 3,130,007. Proposed modifications of this zeolite include the production of ultrastable Y (U.S. Pat. No. 3,536,605) and ultrahydrophobic Y (Great Britain patent No. 2,014,970). In general, such modifications, depending in part upon the particular treatment involved in the modification, result in a reduction of the unit cell size of the zeolite.
In European patent No. B-70,824 there are described hydrocracking catalysts based on a specific type of ultrahydrophobic Y zeolite, particularly a zeolite known as LZ-10. The catalyst support for these catalysts, in addition to specific zeolites having a characteristic water adsorption capacity of less than 8% by weight based on the zeolite, contains a dispersion of silica-alumina particles in a gamma-alumina matrix and no more than a small amount of a binder. The catalysts produced from these supports are said to be an improvement over the non-zeolitic catalysts containing a similar dispersion disclosed in U.S. Pat. No. 4,097,365. It would be of advantage, however, to have hydroprocessing catalysts which provide improved selectivity and stability, as compared to conventional hydrocracking catalysts, while substantially maintaining the activity of the known catalysts.